1. Field of the Invention
This invention relates to a camera having a photosensor for controlling a photographic exposure, and, more particularly, to a control mechanism for regulating infrared (IR) impinging upon the photosensor to refine the control of a flash exposure.
2. Description of the Prior Art
Cameras having a photosensor for regulating an exposure are well known in the photographic art. The photosensor produces an amount of current that is related to light impinging upon it. When a camera shutter is open, the current charges a capacitor. When the capacitor is charged to a predetermined voltage representing a desired exposure, an exposure terminating signal is produced. In the case of a chemical flash exposure, an electromagnet, responsive to the exposure termination signal, is actuated to close the shutter. In the case of an electronic strobe flash exposure, a circuit is energized to quench the electronic flash.
Grass and green foliage reflect relatively high amounts of IR. To prevent a photosensor that is sensitive both to IR and to visible light from prematurely charging the capacitor and closing the shutter in outdoor photography, it is known to use a filter to block IR from the photosensor. U.S. Pat. No. 4,040,070, which is assigned to the assignee of the present invention, describes such an arrangement.
A photographer may choose to use flash illumination when taking pictures outdoors. The flash illumination provides what is commonly known as "fill-flash" to soften dark shadows, which occur in bright sunlight.
In the exposure control apparatus described in U.S. Pat. No. 4,040,070, a flash-sensing member moves the filter from its IR-blocking position whenever a flash exposure is to be taken, which normally occurs indoors. Therefore, an outdoor flash picture can be underexposed because IR from foliage can impinge upon the photosensor and cause the shutter to close prematurely.